Oil-free compressor crankcase cooling arrangement

ABSTRACT

An oil-free compressor crankcase cooling arrangement includes a compressor crankcase, at least one piston cylinder supported in the compressor crankcase, a crankshaft assembly supported by the compressor crankcase and linked to a piston of the at least one piston cylinder by a connecting rod, at least one inlet valve supported on and in fluid communication with the compressor crankcase, and at least one outlet valve supported on and in fluid communication with the compressor crankcase. A cooling cross-flow of air is established between the at least one inlet valve and the at least one outlet valve to cool the compressor crankcase. The at least one inlet valve and the at least one outlet valve include check valves. A first nozzle is positioned on the at least one inlet valve, and a second nozzle is positioned on the at least one outlet valve.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/990,934, filed May 9, 2014, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to the field of air compressors adapted for use on rail vehicles for supplying compressed air to pneumatic units associated with the rail vehicle and, in particular, to an oil-free compressor crankcase cooling arrangement for maintaining a safe operating temperature within the crankcase.

2. Description of Related Art

By design, an oil-free compressor utilizes specially designed bearings and composite sealing materials to allow the air compressor to operate without lubrication. An example of one such oil-free air compressor for a rail vehicle is disclosed in U.S. patent application Ser. No. 14/030,588 to Kapadia et al. filed on Sep. 18, 2013, incorporated herein in its entirety. While the specialized components and materials allow the bearing surfaces to survive the internal loading within the air compressor without lubrications, they do not benefit from the cooling effects that are provided by a large sump of oil included in an oil-flooded air compressor. Therefore, internal cooling must be provided by alternative means.

There are two common preexisting methods for achieving improved cooling within the crankcase of an oil-free air compressor. The first method is to not seal the crankcase and allow air to naturally move into and out of the crankcase. The second method is to draw the compressor inlet air through the crankcase prior to being introduced into the low pressure cylinders for compression.

There are several deficiencies to using the first method of allowing air to naturally move into and out of the crankcase. By leaving the crankcase open to atmosphere, contamination and debris from the surrounding environment is easily pulled into the crankcase and increases the wear of the bearing surfaces, especially the piston ring and cylinder surface that are more prone to contamination. Further, the open crankcase does not create a cooling flow through the crankcase but, instead, creates a wafting-like effect where the same air is pulled in and pushed out of the crankcase. This fails to cool the internal components of the air compressor as efficiently as possible since the hot air pushed out of the air compressor is not moved away from the crankcase.

There are also several deficiencies in using the second method of drawing compressor inlet air through the crankcase prior to being introduced into the low pressure cylinders for compression. By pulling all of the inlet air through the crankcase before entering the first stage of compression, the second method does create a positive flow of fresh air through the crankcase that can be directed from a single inlet point to a single discharge point. However, when the air is routed through the crankcase prior to entering the first stage cylinder, the temperature of the air entering the compressor is higher than it would be if pulled directly into the cylinder. This has at least two effects on the air compressor. Firstly, any of the heat taken out of the crankcase is put back into the compressor within the primary compressing flow path resulting in a higher first stage component temperature. This will ultimately lead to a reduced life span for the inner air compressor components. Further, the increased temperature at the compressor inlet will result in a lower compressor efficiency as the inlet air temperature is inversely proportional to compressor efficiency. Secondly, another deficiency becomes apparent if the air compressor utilizes head unloaders that are a common means to operate an air compressor in an idle mode (not compressing air). In this cycle, the head unloaders typically act to mechanically hold the inlet valves open. By holding the inlet valves open, the air compressor continues to rotate but will not compress air, as the atmospheric air pulled in during the intake stroke is pushed back to atmosphere through the inlet valves during what is normally the compression stroke. As the same air is cycled in and out of the cylinder, the temperature of the air increases during the unloaded cycle. If the cylinder inlet air is routed through the crankcase prior to the atmospheric connection, then the air in the crankcase will be pulled into the first stage cylinder then pushed back into the case during the unloaded cycle. Therefore, the air temperature within the case will increase in temperature during the unloaded cycle similar to the air at the cylinder inlet that increases during the unloaded cycle in any common reciprocating air compressor with head unloaders. Lastly, pulling the inlet air through the crankcase prior to introducing the air into the first stage cylinder may result in contamination from the crankcase being spread into the first stage cylinder. This includes wear debris from the piston rings and excess grease released from the sealed bearings that are both typical occurrences in an oil-free compressor. This contamination will wear on the valves of the air compressor and reduce the life span of the valves.

There is a current need for an oil-free air compressor crankcase cooling arrangement that increases the cooling of the crankcase without increasing the contamination of the internal components of the crankcase. There is also a current need for an oil-free air compressor crankcase cooling arrangement that maximizes the life of the internal dynamic components while maintaining the crankcase at a safe operating temperature.

SUMMARY OF THE INVENTION

In one embodiment, an oil-free compressor crankcase cooling arrangement for a rail vehicle includes a compressor crankcase, at least one piston cylinder supported in the compressor crankcase, a crankshaft assembly supported by the compressor crankcase and linked to a piston of the at least one piston cylinder by a connecting rod, at least one inlet valve supported on and in fluid communication with the compressor crankcase, and at least one outlet valve supported on and in fluid communication with the compressor crankcase. A cooling cross-flow of air is established between the at least one inlet valve and the at least one outlet valve to cool the compressor crankcase.

The at least one inlet valve and the at least one outlet valve may include check valves. A first nozzle may be positioned on the at least one inlet valve, and a second nozzle may be positioned on the at least one outlet valve. An inlet air filter may be positioned on the at least one inlet valve. The inlet air filter may protect the compressor crankcase from contamination and debris. An inlet air filter may be positioned on the first nozzle of the at least one inlet valve. The inlet air filter may protect the compressor crankcase from contamination and debris. The compressor crankcase may define a cavity for housing the crankshaft assembly. The cooling cross-flow of air may be directed through the cavity of the compressor crankcase from a first side of the compressor crankcase to an opposing, second side of the compressor crankcase. The at least one inlet valve may be supported on a first side of the compressor crankcase and the at least one outlet valve may be supported on an opposing, second side of the compressor crankcase. The at least one inlet valve may be opened as air is pulled into the compressor crankcase during an upstroke of the at least one piston cylinder. The at least one outlet valve may be opened as air is pushed out of the compressor crankcase during a downstroke of the at least one piston cylinder. An inloader valve assembly may be positioned on the at least one piston cylinder and may be configured to exhaust pressurized fluid from the at least one piston cylinder.

In another embodiment, a method of cooling an oil-free compressor crankcase of a rail vehicle includes the steps of providing an oil-free compressor including a compressor crankcase, at least one piston cylinder supported in the compressor crankcase, a crankshaft assembly supported by the compressor crankcase and linked to a piston of the at least one piston cylinder by a connecting rod, at least one inlet valve supported on and in fluid communication with the compressor crankcase, and at least one outlet valve supported on and in fluid communication with the compressor crankcase; pulling air into the compressor crankcase via the at least one inlet valve; directing the air through the compressor crankcase; and pushing the air out of the compressor crankcase via the at least one outlet valve.

A further step of the method may include opening the at least one inlet valve during an upstroke of the at least one piston cylinder. Air may be pulled into the compressor crankcase through the open inlet valve. A further step of the method may include opening the at least one outlet valve during a downstroke of the at least one piston cylinder. Air may be pushed out of the compressor crankcase through the open outlet valve. A further step of the method may include establishing a cooling cross-flow of air that is directed from a first side of the compressor crankcase, over the crankshaft assembly, and out of an opposing, second side of the compressor crankcase. The at least one inlet valve may be supported on the first side of the compressor crankcase. The at least one outlet valve may be supported on the opposing, second side of the compressor crankcase. A first nozzle may be positioned on the at least one inlet valve and a second nozzle may be positioned on the at least one outlet valve. Still further steps of the method may include providing an inlet air filter on the at least one inlet valve; and filtering the air that is pulled into the compressor crankcase via the at least one inlet valve using the inlet air filter. Further steps of the method may include providing an inlet air filter on the first nozzle of the at least one inlet valve; and filtering the air that is pulled into the compressor crankcase via the at least one inlet valve using the inlet air filter. The at least one inlet valve and the at least one outlet valve may include check valves. The at least one inlet valve may be supported on the compressor crankcase on a first side of the at least one piston cylinder. The at least one outlet valve may be supported on the compressor crankcase on an opposing second side of the at least one piston cylinder. A further step of the method may include providing an unloader valve assembly on the at least one piston cylinder. Still a further step of the method may include exhausting fluid from the at least one piston cylinder via the unloader valve assembly.

Further details and advantages will be understood from the following detailed description read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of an oil-free air compressor including a crankcase cooling arrangement in accordance with this disclosure.

FIG. 2 is a rear perspective view of the oil-free air compressor of FIG. 1.

FIG. 3 is a cross-sectional view of an oil-free air compressor including a crankcase cooling arrangement in accordance with another embodiment of this disclosure.

FIG. 4 is another cross-sectional view of the oil-free air compressor of FIG. 3 in which a piston cylinder is on a downstroke.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of the description hereinafter, spatial orientation terms, as used, shall relate to the referenced embodiment as it is oriented in the accompanying drawings, figures, or otherwise described in the following detailed description. However, it is to be understood that the embodiments described hereinafter may assume many alternative variations and configurations. It is also to be understood that the specific components, devices, features, and operational sequences illustrated in the accompanying drawings, figures, or otherwise described herein are simply exemplary and should not be considered as limiting.

The present disclosure is directed to, in general, an oil-free compressor crankcase cooling arrangement and, in particular, to an oil-free compressor crankcase cooling arrangement including at least two valves used to create a cross-flow of cooling air through the compressor crankcase. Certain preferred and non-limiting embodiments of the components of the cooling arrangement are illustrated in FIGS. 1-4.

Referring to FIGS. 1-4, an air compressor 10 according to one embodiment of the disclosure is shown. As shown, the air compressor 10 is a multi-cylinder air compressor 10 including a first piston cylinder 20, a second piston cylinder 30, a third piston cylinder 40, and a fourth piston cylinder 50. In one embodiment, the air compressor 10 is an oil-free air compressor for a rail vehicle (not shown). The first piston cylinder 20, the second piston cylinder 30, the third piston cylinder 40, and the fourth piston cylinder 50 are supported by a compressor housing or crankcase 12 and each are driven by a crankshaft assembly 60 disposed within the compressor crankcase 12 and rotationally supported by the compressor crankcase 12. The compressor crankcase 12 may define a cavity 14 therein for housing the crankshaft assembly 60. The foregoing components of the air compressor 10 are described in detail herein. A method of cooling the compressor crankcase 12 is described in further detail hereinbelow. The air compressor 10 may have a pentagonal-shaped cross-section. A support member 13 may be fastened to a bottom surface of the air compressor 10. The support member 13 may be used to mount the air compressor 10 on a locomotive or rail vehicle (not shown).

The first piston cylinder 20, the second piston cylinder 30, the third piston cylinder 40, and the fourth piston cylinder 50 may be of substantially similar construction with the first piston cylinder 20 operating as the first cylinder, the second piston cylinder 30 operating as the second cylinder, the third piston cylinder 40 operating as the third cylinder, and the fourth piston cylinder 50 operating as the fourth cylinder in the multi-cylinder air compressor 10. In one embodiment, the first piston cylinder 20, the second piston cylinder 30, the third piston cylinder 40, and the fourth piston cylinder 50 may be radially configured about a longitudinal axis of the air compressor 10. The piston cylinders 20, 30, 40, 50 may interface with an outer circumference of the air compressor 10.

As shown in FIGS. 3 and 4, the first piston cylinder 20 includes a cylindrical housing 21 that has a first end 22 a adapted to be inserted into a corresponding opening, as described herein, in the compressor crankcase 12 and a second end 22 b. The cylindrical housing 21 is formed with a flange 23 located proximal the first end 22 a for interfacing with the exterior of the compressor crankcase 12. Heat-dissipating fins 24 may be provided about the cylindrical housing 21, and the cylindrical housing 21 may be formed of any suitable material providing sufficient strength and heat-dissipating characteristics such as aluminum.

A cylinder head 25 is secured to the second end 22 b of the cylindrical housing 21. The cylinder head 25 generally comprises an air connecting unit 26 and an unloader cap 29 mechanically fastened to a top surface of the air connecting unit 26. The air connecting unit 26 includes a first air channel 27 and a second air channel 28. The air connecting unit 26 may be formed of any suitable material providing sufficient strength and heat transfer characteristics such as aluminum. The unloader cap 29 houses an unloader piston (not shown) that mechanically holds the inlet side of the valve assembly (not shown) open when a pneumatic signal is piloted to the valve assembly. It is also to be understood that an electric signal may be used to pilot the valve assembly. When activated, the air compressor 10 will continue to operate without compressing air, thereby cooling the cavity 14 of the air compressor 10.

The first piston cylinder 20 may further include a first piston 70 that is reciprocally operable within the cylindrical housing 21. The piston 70 includes a first end 72 a and a second end 72 b, and is made of any suitable material providing sufficient strength and heat transfer characteristics such as aluminum. The piston 70 is operatively connected to the crankshaft assembly 60 via a connecting rod 74. A cavity 76 may be defined in the cylindrical housing 21 to hold the piston 70. In operation, the piston 70 operates in a reciprocating movement which is generated via rotation of the crankshaft assembly 60. Air is drawn into the cavity 76 of the cylindrical housing 21 of the first piston cylinder 20 via one of the air channels 27, 28 as a result of the downward movement of the piston 70. A valve assembly (not shown) may be associated with the cylinder head 25 and includes a portion that is opened during the downward movement of the piston 70, drawing air into the cylindrical housing 21, and closes during the upward movement. Further, the valve assembly may include another portion that closes during the downward movement of the piston 70 and opens during the upward movement of the piston 70, whereby air in the cylindrical housing 21 is compressed and is guided out of the cylindrical housing 21.

As noted previously, the second piston cylinder 30, the third piston cylinder 40, and the fourth piston cylinder 50 have a substantially similar construction to the first piston cylinder 20.

Referring to FIGS. 1 and 2, a first inlet valve 80 and a second inlet valve 82 are supported on a first side of the compressor crankcase 12. A first outlet valve 90 and a second outlet valve 92 may be supported on an opposing, second side of the compressor crankcase 12. The first inlet valve 80, the second inlet valve 82, the first outlet valve 90, and the second outlet valve 92 may be in fluid communication with the compressor crankcase 12. In one embodiment, the first inlet valve 80, the second inlet valve 82, the first outlet valve 90, and the second outlet valve 92 may be check valves. In one embodiment, the first inlet valve 80, the second inlet valve 82, the first outlet valve 90, and the second outlet valve 92 may be ball-type check valves. In another embodiment, the first inlet valve 80, the second inlet valve 82, the first outlet valve 90, and the second outlet valve 92 may include an elastomer valve element (not shown) positioned between a seat (not shown) and guide member (not shown). This type of check valve is commonly known as a “flapper” style check valve. It is to be understood, however, that the use of alternative types of check valves are contemplated, such as a diaphragm check valve, a swing check valve, and a lift check valve, among others. In one embodiment, the first inlet valve 80, the second inlet valve 82, the first outlet valve 90, and the second outlet valve 92 may be used to establish a cooling cross-flow of air 16 between one another to cool the compressor crankcase 12. Although only two inlet valves and two outlet valves are shown in the drawings, it is contemplated that fewer or additional inlet valves and outlet valves may be supported on the compressor crankcase 12 to provide a reduced or greater amount of air for the cooling cross-flow 16 through the compressor crankcase 12. As shown in FIGS. 1 and 2, the first inlet valve 80 and the second inlet valve 82 may be positioned parallel to one another, and the first outlet valve 90 and the second outlet valve 90 may be positioned parallel to one another. It is also to be understood, however, that the first inlet valve 80 and the second inlet valve 82 may be positioned in series with one another, and the first outlet valve 90 and the second outlet valve 92 may be positioned in series with one another. The configuration of the valves may be used according to the capacity needed in the air compressor 10 and to provide redundancy.

In one embodiment, the first inlet valve 80 and the second inlet valve 82 may be supported on a lower portion of the compressor crankcase 12. The first outlet valve 90 and the second outlet valve 92 may be supported on an opposing, lower portion of the compressor crankcase 12. In one embodiment, the first inlet valve 80 and the second inlet valve 82 may be supported on the compressor crankcase 12 adjacent the first piston cylinder 20. The first outlet valve 90 and the second outlet valve 92 may be supported on the compressor crankcase 12 adjacent the fourth piston cylinder 50. Using this arrangement of the first inlet valve 80, the second inlet valve 82, the first outlet valve 90, and the second outlet valve 92, the cooling cross-flow of air 16 may be directed through the cavity 14 of the compressor crankcase 12 from the first side of the compressor crankcase 12 to the opposing, second side of the compressor crankcase 12. The cooling cross-flow of air 16 is directed over the crankshaft assembly 60 to provide cooling for the components of the crankshaft assembly 60 and the compressor crankcase 12. To establish this cooling cross-flow of air 16 in the compressor crankcase 12, air is pulled into the compressor crankcase 12 via the first inlet valve 80 and the second inlet valve 82. During an upstroke of the piston 70 in the cylindrical housing 21 of the first piston cylinder 20, the first inlet valve 80 and the second inlet valve 82 are opened by the air that is pulled into the compressor crankcase 12. The first inlet valve 80 and the second inlet valve 82 may be selected and/or adjusted according to the desired amount of air pressure that is necessary to open the first inlet valve 80 and the second inlet valve 82. During the upstroke of the piston 70 in the cylindrical housing 21 of the first piston cylinder 20, the first outlet valve 90 and the second outlet valve 92 are kept closed. In one embodiment, the cooling cross-flow of air 16 is then directed diagonally through the cavity 14 of the crankcase assembly 12 towards the first outlet valve 90 and the second outlet valve 92. During a downstroke of the piston 70 in the cylindrical housing 21 of the first piston cylinder 20, the cooling cross-flow of air 16 is pushed out of the first outlet valve 90 and the second outlet valve 92 to atmosphere. During the downstroke of the piston 70 in the cylindrical housing 21 of the first piston cylinder 20, the first inlet valve 80 and the second inlet valve 82 are kept closed. The first outlet valve 90 and the second outlet valve 92 may be selected and/or adjusted according to the desired amount of air pressure that is necessary to open the first outlet valve 90 and the second outlet valve 92. The total change of volume in the air compressor 10 is a summation of all of the piston movement within the air compressor 10. Therefore, it is the total volume changed by reciprocating movement of the first piston cylinder 20, the second piston cylinder 30, the third piston cylinder 40, and the fourth piston cylinder 50, combined. This configuration and operation of the air compressor 10 ensures that the maximum amount of crankcase volume change is achieved without sacrificing other air compressor 10 characteristics. By combining the change in volume of all of the piston cylinders 20, 30, 40, 50, during rotation of the crankshaft assembly 60, a maximum volume of air may be used to cool the air compressor 10.

While FIGS. 1 and 2 depict the use of two inlet valves 80, 82 and two outlet valves 90, 92, it is also to be understood that only one inlet valve 80 and one outlet valve 90 may be used, as shown in FIGS. 3 and 4.

Referring now to FIGS. 3 and 4, a first nozzle 100 may be positioned on the first inlet valve 80 and/or the second inlet valve 82. The first nozzle 100 may be used to direct the flow of air into the first inlet valve 80 and/or the second inlet valve 82 during the upstroke of the piston 70 in the cylindrical housing 21 of the first piston cylinder 20. A second nozzle 110 may be positioned on the first outlet valve 90 and/or the second outlet valve 92. The second nozzle 110 may be used to direct the flow away from the compressor crankcase 12 to avoid directing the exhausted hot air back towards the compressor crankcase 12. It is to be understood that different types of nozzles may be used in place of the first nozzle 100 and the second nozzle 110, such as nozzles with a wider or narrower inlet or nozzles with a different cross-sectional shape. Further, although FIGS. 3 and 4 only depict the use of the first inlet valve 80 and the first outlet valve 90, it is to be understood that the second inlet valve 82 and the second outlet valve 92 may be used as well. Nozzles may also be positioned on these valves as well.

With continued reference to FIGS. 3 and 4, an inlet air filter 120 may be operatively connected to the first inlet valve 80 and/or the second inlet valve 82. The inlet air filter 120 may be any standard inlet air filter commercially available that provides a screening function to remove contamination and debris from the air that is pulled into the compressor crankcase 12 through the first inlet valve 80 and/or the second inlet valve 82. The inlet air filter 120 provides filtering capabilities to the air compressor 10 by removing debris and other contamination that may create wear on the crankshaft assembly 60 and components of the piston cylinders 20, 30, 40, 50. In one embodiment, the inlet air filter 120 may be positioned on an end of the first nozzle 100. During use of the air compressor 10, air is pulled into the cavity 14 of the compressor crankcase 12 first through the inlet air filter 120, then through the first nozzle 100, and finally through the first inlet valve 80 and/or the second inlet valve 82.

Although a description of the first inlet valve 80 and the first outlet valve 90 being operatively positioned with the first piston cylinder 20 is provided, one of skill in the art will recognize that the first inlet valve 80 and the first outlet valve 90 may also be operatively positioned at different positions on the compressor crankcase 12. The first inlet valve 80 and the first outlet valve 90 may be operatively positioned with another piston cylinder 30, 40, 50. Further, the first inlet valve 80 and the first outlet valve 90 may be positioned adjacent the first piston cylinder 20 and the fourth piston cylinder 50, respectively. The arrangement of the inlet valve 80 and the outlet valve 90 would be substantially similar to the arrangement described above in connection with the first piston cylinder 20.

A method of cooling the compressor crankcase 12 is also described herein with reference to FIGS. 3 and 4. In one embodiment, this method includes the step of providing an air compressor 10 as described hereinabove. During use of the cooling method, air from atmosphere is pulled into the cavity 14 of the compressor crankcase 12 via the first inlet valve 80. The air is used as a cooling cross-flow of air 16 that is directed from the first inlet valve 80 to the first outlet valve 90. The cooling cross-flow of air 16 is directed through the cavity 14 of the compressor crankcase 12, thereby flowing over the components of the crankshaft assembly 60 and the piston cylinders 20, 30, 40, 50. After the cooling cross-flow of air 16 is directed through the cavity 14 of the compressor crankcase 12, the air is pushed out of the compressor crankcase 12 via the first outlet valve 90. As the air is directed over the crankshaft assembly 60 and the components of the piston cylinders 20, 30, 40, 50, the components are cooled by the air. The heat generated by the components is transferred to the cooling cross-flow of air 16 and carried out of the compressor crankcase 12. In one embodiment, the first inlet valve 80 and the first outlet valve 90 may be check valves, as described hereinabove. The first inlet valve 80 may be supported on a first side of the compressor crankcase 12. The first outlet valve 90 may be supported on an opposing, second side of the compressor crankcase 12.

As the pistons 20, 30, 40, 50 of the air compressor 10 move in and out of their respective piston cylinders, the total volume within the compressor crankcase 12 changes through a single rotation of the crankshaft assembly 60 provided the cylinders 20, 30, 40, 50 are not perfectly out of phase and of the same diameter. In one embodiment, the first inlet valve 80 is opened during an upstroke of the piston 70 in the cylindrical housing 21 of the first piston cylinder 20. The pressure exerted by the air that is pulled into the compressor crankcase 12 pushes open the first inlet valve 80. In one embodiment, air may be pulled into the compressor crankcase 12 via the first inlet valve 80 until a maximum volume of the compressor crankcase 12 is filled. In one embodiment, the first outlet valve 90 may be opened during a downstroke of the piston 70 in the cylindrical housing 21 of the first piston cylinder 20. The pressure exerted by the air that is pushed through and out of the cavity 14 of the compressor crankcase 12 pushes open the first outlet valve 90, thereby allowing the air to vent to atmosphere. In one embodiment, air is pushed out of the compressor crankcase 12 via the first outlet valve 90 until a minimum volume of the compressor crankcase 12 remains. Using the described method, the cooling cross-flow of air 16 may be directed from a first side of the compressor crankcase 12, over the crankshaft assembly 60, and out of an opposing, second side of the compressor crankcase 12. In this embodiment, the first inlet valve 80 is supported on the first side of the compressor crankcase 12 and the first outlet valve 90 is supported on the opposing, second side of the compressor crankcase 12. Although the operation of the cooling method of the air compressor 10 is described in relation to the first piston cylinder 20, it is to be understood that the cooling method is a cumulative effect of the reciprocating movement of all of the piston cylinders 20, 30, 40, 50 that creates the cooling cross-flow of air 16. The second piston cylinder 30, the third piston cylinder 40, and the fourth piston cylinder 50 operating in a similar manner to the first piston cylinder 20 to create the cross-flow of air 16. It is also to be understood that the first inlet valve 80 and the first outlet valve 90 may be positioned near one of the second piston cylinder 30, the third piston cylinder 40, or the fourth piston cylinder 50 to provide the same cooling effect in the air compressor 10.

In one embodiment of the method, the first nozzle 100 may be positioned on the first inlet valve 80 and the second nozzle 110 may be positioned on the first outlet valve 90. The first nozzle 100 may be configured to direct the air from atmosphere into the first inlet valve 80. The second nozzle 110 may be configured to direct the air from the first outlet valve 90 to atmosphere. The second nozzle 110 directs the air, whose temperature has risen due to the heat transferred from the compressor crankcase 12 components, away from the compressor crankcase 12 to atmosphere.

In another embodiment of the method, the inlet air filter 120 may be operatively connected to the first inlet valve 80. The air that is pulled into the first inlet valve 80 may be filtered by the inlet air filter 120 to remove any contamination or debris from the air, so as not to contaminate or wear the inner components of the air compressor 10. The inlet air filter 120 may also be positioned on an end of the first nozzle 100 connected to the first inlet valve 80.

As explained hereinabove, although a description of a method of using the first inlet valve 80 and the first outlet valve 90 with the first piston cylinder 20 to cool the inner components of the compressor crankcase 12 is provided, one of skill in the art will recognize that the method may also be performed at different positions on the compressor crankcase 12. The first inlet valve 80 and the first outlet valve 90 may be operatively positioned with another piston cylinder 30, 40, 50. Alternatively, the first inlet valve 80 and the first outlet valve 90 may be positioned adjacent to the first piston cylinder 20 and the fourth piston cylinder 50, respectively. It is also to be understood that the second inlet valve 82 and the second outlet valve 92 may be used to create a larger cooling cross-flow of air 16 through the compressor crankcase 12. The arrangement and operation of the inlet valve 80 and the outlet valve 90 would be substantially similar to the arrangement described above in connection with the first piston cylinder 20.

By using the method described hereinabove, there is no effect on the inlet air temperatures that are provided. Therefore, the first inlet valve 80 and the first outlet valve 90 are able to provide a directed positive flow through the compressor crankcase 12 without reducing the overall efficiency of the air compressor 10, unlike if the inlet air was first routed through the compressor crankcase 12. Further, the air at the first inlet valve 80 will not be pre-heated upon entering the compressor crankcase 12, resulting in lower first stage temperatures. The air compressor 10 described hereinabove includes a multi-cylinder arrangement that maximizes the total change in the compressor crankcase 12 volume per revolution of the crankshaft assembly 60, without sacrificing the dynamic balance of the air compressor 10. In addition, the total crankshaft assembly 60 torque pulse per each revolution is reduced, while still maintaining a small overall size envelope for the air compressor 10.

While an embodiment of an oil-free compressor crankcase cooling arrangement is shown in the accompanying figures and described hereinabove in detail, other embodiments will be apparent to, and readily made by, those skilled in the art without departing from the scope and spirit of the invention. Accordingly, the foregoing description is intended to be illustrative rather than restrictive. The invention described hereinabove is defined by the appended claims and all changes to the invention that fall within the meaning and the range of the equivalency of the claims are to be embraced within their scope. 

The invention claimed is:
 1. An oil-free compressor crankcase cooling arrangement for a rail vehicle, comprising: a compressor crankcase; at least one piston cylinder supported in the compressor crankcase; a crankshaft assembly supported by the compressor crankcase and linked to a piston of the at least one piston cylinder by a connecting rod; at least one inlet valve supported on and in fluid communication with the compressor crankcase; and at least one outlet valve supported on and in fluid communication with the compressor crankcase, wherein a cooling cross-flow of air is established between the at least one inlet valve and the at least one outlet valve to cool the compressor crankcase.
 2. The crankcase cooling arrangement as claimed in claim 1, wherein the at least one inlet valve and the at least one outlet valve comprise check valves.
 3. The crankcase cooling arrangement as claimed in claim 1, further comprising a first nozzle positioned on the at least one inlet valve, and a second nozzle positioned on the at least one outlet valve.
 4. The crankcase cooling arrangement as claimed in claim 1, further comprising an inlet air filter operatively connected to the at least one inlet valve, wherein the inlet air filter protects the compressor crankcase from contamination and debris.
 5. The crankcase cooling arrangement as claimed in claim 3, further comprising an inlet air filter positioned on the first nozzle of the at least one inlet valve, wherein the inlet air filter protects the compressor crankcase from contamination and debris.
 6. The crankcase cooling arrangement as claimed in claim 1, wherein the compressor crankcase defines a cavity for housing the crankshaft assembly, and wherein the cooling cross-flow of air is directed through the cavity of the compressor crankcase from a first side of the compressor crankcase to an opposing, second side of the compressor crankcase.
 7. The crankcase cooling arrangement as claimed in claim 1, wherein the at least one inlet valve is supported on a first side of the compressor crankcase and the at least one outlet valve is supported on an opposing, second side of the compressor crankcase.
 8. The crankcase cooling arrangement as claimed in claim 1, wherein the at least one inlet valve is opened as air is pulled into the compressor crankcase during an upstroke of the at least one piston cylinder.
 9. The crankcase cooling arrangement as claimed in claim 1, wherein the at least one outlet valve is opened as air is pushed out of the compressor crankcase during a downstroke of the at least one piston cylinder.
 10. The crankcase cooling arrangement as claimed in claim 1, further comprising an unloader valve assembly positioned on the at least one piston cylinder configured to exhaust pressurized fluid from the at least one piston cylinder.
 11. A method of cooling an oil-free compressor crankcase of a rail vehicle, comprising the steps of: a) providing an oil-free compressor, comprising: a compressor crankcase; at least one piston cylinder supported in the compressor crankcase; a crankshaft assembly supported by the compressor crankcase and linked to a piston of the at least one piston cylinder by a connecting rod; at least one inlet valve supported on and in fluid communication with the compressor crankcase; and at least one outlet valve supported on and in fluid communication with the compressor crankcase; b) pulling air into the compressor crankcase via the at least one inlet valve; c) directing the air through the compressor crankcase; and d) pushing the air out of the compressor crankcase via the at least one outlet valve.
 12. The method of cooling a compressor crankcase as claimed in claim 11, further comprising the step of opening the at least one inlet valve during an upstroke of the at least one piston cylinder, wherein air is pulled into the compressor crankcase through the open inlet valve.
 13. The method of cooling a compressor crankcase as claimed in claim 11, further comprising the step of opening the at least one outlet valve during a downstroke of the at least one piston cylinder, wherein air is pushed out of the compressor crankcase through the open outlet valve.
 14. The method of cooling a compressor crankcase as claimed in claim 11, further comprising the step of establishing a cooling cross-flow of air that is directed from a first side of the compressor crankcase, over the crankshaft assembly, and out of an opposing second side of the compressor crankcase, wherein the at least one inlet valve is supported on the first side of the compressor crankcase, and wherein the at least one outlet valve is supported on the opposing, second side of the compressor crankcase.
 15. The method of cooling a compressor crankcase as claimed in claim 11, the oil-free compressor further comprising a first nozzle positioned on the at least one inlet valve and a second nozzle positioned on the at least one outlet valve.
 16. The method of cooling a compressor crankcase as claimed in claim 11, further comprising the steps of: providing an inlet air filter operatively connected to the at least one inlet valve; and filtering the air that is pulled into the compressor crankcase via the at least one inlet valve using the inlet air filter.
 17. The method of cooling a compressor crankcase as claimed in claim 15, further comprising the steps of: providing an inlet air filter on the first nozzle of the at least one inlet valve; and filtering the air that is pulled into the compressor crankcase via the at least one inlet valve using the inlet air filter.
 18. The method of cooling a compressor crankcase as claimed in claim 11, wherein the at least one inlet valve and the at least one outlet valve comprise check valves.
 19. The method of cooling a compressor crankcase as claimed in claim 11, wherein the at least one inlet valve is supported on the compressor crankcase on a first side of the at least one piston cylinder, and wherein the at least one outlet valve is supported on the compressor crankcase on an opposing second side of the at least one piston cylinder.
 20. The method of cooling a compressor crankcase as claimed in claim 11, further comprising the steps of: providing an unloader valve assembly on the at least one piston cylinder, and exhausting fluid from the at least one piston cylinder via the unloader valve assembly. 